1. Field of the Invention
The present invention relates to a room-temperature curable organopolysiloxane composition which is ideal as a coating material, and particularly to a room-temperature curable organopolysiloxane which generates an antifouling coating and is ideal for applying to ships, port installations, buoys, pipelines, bridges, undersea bases, seabed oil field excavation equipment, water supply pipes for power generation stations, nets for aquatic farming, and fixed nets and the like (hereafter jointly described as “underwater structures”) to prevent the adhesion and growth of aquatic organisms on the surface of such structures.
2. Description of the Prior Art
Many room-temperature curable silicone rubber compositions which generate rubber like elastic bodies at room temperature are already known. Cured rubbers obtained from room-temperature curable silicone rubber compositions display superior weather resistance, durability, heat resistance and cold resistance when compared with other organic-based rubbers, and are consequently widely used in many fields, particularly within the field of construction, where they are used for a variety of applications including as glass adhesives, adhesives between metals and glass, and as sealants between masonry joints. Furthermore, in recent years, they have also become widely used as coatings for building structures, production plants, and on the internal surfaces and external surfaces of water pipes.
However, the organopolysiloxanes which constitute one of the main components of these types of room-temperature curable silicone rubber compositions become easily charged and are prone to adsorbing dust from the atmosphere, and as a result, the surface of the cured sealing materials or coating materials became heavily soiled over time and lose their esthetic appearance. Examples of methods aimed at resolving this problem have proposed the addition of a surfactant-containing a polyoxyethylene group, a sorbitan residue or a disaccharide residue to the room-temperature curable silicone rubber composition (Japanese Laid-open publication (kokai) No. 56-76452 (JP56-76452A), and Japanese Laid-open publication (kokai) No. 56-76453 (JP56-76453A)). However, in order to obtain satisfactory effects with these methods, large quantities of the surfactant need to be added, causing a deterioration in the adhesion, which represents one of the most important functions for a sealing material or a coating material formed from a room-temperature curable silicone rubber composition.
Furthermore, when an underwater structure is installed or enters service, then aquatic organisms which live in the water of the river or sea, such as barnacles, ascidiacea, serupura, mussels, fresh-water mussels, bugula neritina, green laver and sea lettuce adhere and start growing on the structure, from the water surface contact region through to the submerged surfaces of the structure, which can generate a variety of problems. For example, when organisms adhere to the hull of a vessel, the friction resistance with the water increases, causing a reduction in the traveling speed of the ship or vessel, and consequently the fuel consumption required to maintain a constant speed increases, which is economically disadvantageous. Furthermore, when organisms adhere to structures secured either in, or on the surface of the water, such as port installations and the like, then ensuring satisfactory performance of the variety of functions of such structures becomes difficult, and erosion of the structure base material can also become a problem. In addition, when organisms adhere to nets used for aquatic farming, or to fixed nets and the like, then the openings within the net can become blocked causing fish to die.
Examples of countermeasures for preventing the adhesion and growth of aquatic organisms on underwater structures included the application of an antifouling paint containing a toxic antifouling agent such as an organotin compound or cuprous oxide to the structure. Although such measures substantially prevented the adhesion or growth of any aquatic organisms, the fact that the paint used a toxic antifouling agent meant that the environmental and hygiene conditions during production and application of the paint were undesirable, and furthermore when placed in the water, the toxic antifouling agent was gradually eluted from the paint film over time, meaning that there was a danger of polluting the water, and as a result the use of such antifouling paints has now been banned by law.
In contrast, paints which prevent the adhesion and growth of aquatic organisms, but contain no toxic antifouling agents, including non-toxic antifouling paints comprising a room-temperature curable silicone rubber composition to which is added a liquid paraffin or a petrolatum in order to lower the surface tension of the paint film and impart antifouling properties, have already been proposed (Japanese Laid-open publication (kokai) No. 58-13673 (JP58-13673A), Japanese Laid-open publication (kokai) No. 62-84166 (JP62-84166A)). Furthermore, non-toxic antifouling paint compositions which utilize the volumetric shrinkage accompanying the curing of a reaction curing type silicone resin, so that a silicone resin which contains an unreactive polar group and displays poor co-solubility with the aforementioned reaction curing type silicone resin bleeds out to the surface, thereby combining antifouling properties with the low surface tension of the reaction curing type silicone resin, have also been proposed (Japanese Patent publication No. 250398 (JP250398B), Japanese Patent publication No. 2952375 (JP2952375B)). However, in the non-toxic antifouling paint compositions described above, the aforementioned silicone resin which contains an unreactive polar group and displays poor co-solubility utilizes either a silicone resin with a polyoxyethylene group in which ethylene oxide or propylene oxide or the like are added via a C—C linkage to a Si atom, or a silicone resin in which an alkoxy group is introduced at a molecular terminal Si atom via an ethylene oxide or propylene oxide group, and consequently the compositions were unable to provide satisfactory performance in terms of the long term endurance of the antifouling properties.